Process for producing catalyst

ABSTRACT

Disclosed is a method for producing a catalyst, in which physical properties of a dried material or a calcined material in a production process of the catalyst are stable and a change in at least one of a catalyst activity and a selectivity to a target product is small and hence reproducibility of the catalyst is excellent. The present invention is a method for producing a catalyst containing molybdenum, bismuth, and iron, which contains the steps of washing a surface of at least one device equipped in an apparatus for the production of catalyst, to which a solid matter adheres, with a basic solution, and producing the catalyst with the apparatus for the production of catalyst thus washed.

TECHNICAL FIELD

The present invention relates to a method for producing a catalystcontaining molybdenum, bismuth, and iron.

BACKGROUND ART

The catalyst containing molybdenum, bismuth, and iron is known as anoxidation catalyst which is used for producing an unsaturated aldehydeand an unsaturated carboxylic acid through gas-phase catalytic oxidationof propylene, isobutylene, tertiary butyl alcohol (hereinafter,sometimes expressed as “TBA”), or methyl tertiary butyl ether(hereinafter, sometimes expressed as “MTBE”).

For example, in Patent Documents 1 and 2, a method for producing acatalyst is individually disclosed, in which a mixed liquid containing acompound which becomes a raw material of the catalyst is prepared andthe resultant mixed liquid is dried and then calcined.

Patent Document 1: Japanese Patent Application Laid-Open No. Hei8-309,191Patent Document 2: Japanese Patent Application Laid-Open No. Hei8-309,192

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

In a conventional method, when a catalyst is produced repeatedly, it wasnecessary to adjust conditions at the time of molding a dried materialor a calcined material at each production batch because physicalproperties, such as bulk density, of a dried material of a mixed liquidor a calcined material obtained by calcining the dried material changed.Further, there was a case that at least one of a catalyst activity and aselectivity to a target product was deteriorated when the catalystproduction was repeated.

Conventionally, there has been a case that a solid matter containingmolybdenum, bismuth, and iron adheres to a surface of a device equippedin an apparatus for the production of catalyst when the catalyst isproduced, however, such an adherence of the solid matter has notparticularly been recognized as a problem. However, the presentinventors have found that the solid matter is a cause of the change ofthe physical properties of the aforementioned bulk density or thedeterioration of at least one of the catalyst activity and theselectivity to the target product, and thus they have completed thepresent invention.

It is an object of the present invention to provide a method forproducing a catalyst, in which physical properties of a dried materialor a calcined material in a production process of the catalyst arestable and a change in at least one of a catalyst activity and aselectivity to a target product is small and hence reproducibility ofthe catalyst is excellent.

Means for Solving the Problem

The present invention is a method for producing a catalyst comprisingmolybdenum, bismuth, and iron, comprising the steps of:

washing a surface of at least one device equipped in an apparatus forthe production of catalyst, to which a solid matter adheres, with abasic solution; andproducing the catalyst with the apparatus for the production of catalystthus washed.

EFFECT OF THE INVENTION

According to the present invention, a method for producing a catalyst,in which physical properties of a dried material or a calcined materialin a production process of the catalyst are stable and a change in atleast one of a catalyst activity and a selectivity to a target productis small and hence reproducibility of the catalyst is excellent, can beprovided. Further, according to the present invention, the catalyst canbe produced efficiently because a residual material can be reduced bysaving the time of overhaul in the case that an apparatus for theproduction of catalyst is complicatedly assembled.

BEST MODE FOR CARRYING OUT THE INVENTION

As the catalyst containing molybdenum, bismuth, and iron to be producedin the present invention, for example, one to be used for producing anunsaturated aldehyde and an unsaturated carboxylic acid throughgas-phase catalytic oxidation of propylene, isobutylene, TBA, or MTBEwith molecular oxygen, or one to be used for producing acrylonitrilethrough gas-phase catalytic ammoxidation of propylene can be listed.

Hereinafter, the method for producing the catalyst of the presentinvention will be explained with reference to the method for producingthe catalyst for producing an unsaturated aldehyde and an unsaturatedcarboxylic acid, which is one embodiment of the present invention.

The catalyst to be produced is not particularly limited as long as itcontains molybdenum, bismuth, and iron, however, it is preferably theone represented by the following formula (I).

MO_(a) Bi_(b) Fe_(c) M_(d) X_(e) Y_(f) Z_(g) Si_(h) O_(i)  (1)

In the formula (I), Mo, Bi, Fe, Si, and O represent molybdenum, bismuth,iron, silicone, and oxygen, respectively. M represents at least oneelement selected from the group consisting of cobalt and nickel. Xrepresents at least one element selected from the group consisting ofchromium, lead, manganese, calcium, magnesium, niobium, silver, barium,tin, tantalum and zinc. Y represents at least one element selected fromthe group consisting of phosphorus, boron, sulfur, selenium, tellurium,cerium, tungsten, antimony, and titanium. Z represents at least oneelement selected from the group consisting of lithium, sodium,potassium, rubidium, cesium, and thallium. a, b, c, d, e, f, g, h, and irepresent an atomic ratio of each element, respectively, and when a is12, b is from 0.01 o 3, c is from 0.01 to 5, d is from 1 to 12, e isfrom 0 to 8, f is from 0 to 5, g is from 0.001 to 2, h is from 0 to 20,and i is the atomic ratio of oxygen that fulfills the requirement of thevalence of each element mentioned above.

In the present invention, a raw material of an element that composes thecatalyst (hereinafter, expressed as a “catalyst raw material”) is notparticularly limited, however, usually, an oxide of the element thatcomposes the catalyst, a chloride, a hydroxide, a sulfate, a nitrate, acarbonate, or an ammonium salt that can become the oxide of the elementthat composes the catalyst by ignition, or a mixture of these compoundscan be used.

The production of the catalyst can be carried out, for example, byproperly combining the following steps.

Blending step: A step in which a solution or a fluid dispersioncontaining at least one kind of the element that composes the catalyst(hereinafter, expressed as a “blended liquid”) is prepared by blendingat least one kind of the catalyst raw material and a liquid in ablending tank.Mixing step: A step in which a solution or a fluid dispersion containingall the elements that compose the catalyst (hereinafter, expressed as a“raw material liquid”) is prepared by mixing two or more kinds of theblended liquids or by mixing the blended liquid and another catalyst rawmaterial in a mixing tank.Aging step: A step in which the raw material liquid is aged while heatedin an aging tank.Concentrating step: A step in which the raw material liquid isconcentrated in a concentrating tank.Atomizing step: A step in which a solid matter contained in the rawmaterial liquid is atomized in an atomizing tank.

There is a case that a tank equipped with a jacket with which contentsof the tank can be heated or cooled is used as a device such as theblending tank, the mixing tank, the aging tank, the concentrating tank,or the atomizing tank in order to adjust the temperature of the solutionor the fluid dispersion in these steps. In this case, the temperature ofthe contents of the tank is adjusted by causing a heating medium such aswater vapor to exist or flow inside the jacket. Further, a deviceequipped with a heating part such as a heater or a cooling part insidecan be used for the adjustment of the temperature. In the apparatus forthe production of catalyst to be used in the present invention, theblending tank, the mixing tank, the aging tank, the concentrating tank,and the atomizing tank mentioned above are included, however, not onlythese devices but also, for example, a piping, a pump, a strainer, astirring blade, a heater, and the like are included.

In the next place, each production step of the catalyst will beexplained in detail.

(Blending Step)

In the blending step, the blended liquid is prepared by blending atleast one kind of the catalyst raw material and a liquid in a blendingtank. It is preferable to separate the catalyst raw material into two ormore kinds and to prepare two or more kinds of the blended liquids. Themethod for separating the catalyst raw material into two or more kindsis not particularly limited, however, it is preferable to select acombination of the catalyst raw material and the liquid, which does notcause precipitation or gelation of the resulting blended liquid, and itis more preferable to make a blended liquid of a raw material ofmolybdenum and a blended liquid of a raw material of iron separately.

As the blended liquid containing molybdenum, for example, an aqueoussolution obtained by dissolving ammonium molybdate in water can belisted. Further, as the blended liquid containing iron, for example, anaqueous solution obtained by dissolving respective nitrates of iron,bismuth, cobalt, and cesium in dilute nitric acid can be listed.

(Mixing Step)

In the mixing step, the raw material liquid is prepared by mixing two ormore kinds of the blended liquids or by mixing the blended liquid andanother catalyst raw material in a mixing tank. The other catalyst rawmaterial means the catalyst raw material that has not been blended inthe blending step, and it may be a solid such as an oxide or a salt ofan element that composes the catalyst, which is the same as mentionedabove. The combination of the blended liquid and the other catalyst rawmaterial to be mixed in the mixing step is not particularly limited,however, the combination of two or more kinds of the blended liquids ispreferable, the combination of two or more kinds of the blended liquidswhich is not causing precipitation or gelation is more preferable, andabove all, the combination of the blended liquid containing molybdenumand the blended liquid containing iron is particularly preferable. Asthe method for mixing, for example, a method of stirring mixing or amethod of ultrasonic mixing can be listed.

For example, when the blended liquid containing molybdenum and theblended liquid containing iron are mixed, there are many cases thatprecipitation is formed to cause gelation. In this case, precipitatedparticles with the same fine structure such as particle diameter can beobtained by adjusting the mixing time to a fixed value in eachproduction batch. The mixing time on that occasion is preferably 60seconds or more, and the catalyst can be produced with excellentreproducibility by such a mild mixing.

When the blended liquid containing molybdenum and the blended liquidcontaining iron are mixed, it is preferable to mix in such a way thatthe blended liquid containing iron is added to the blended liquidcontaining molybdenum.

(Aging Step)

In the aging step, the raw material liquid is aged while heated in anaging tank. It is preferable that the aging be carried out for 30minutes or more while heated. In that case, the temperature of the rawmaterial liquid is preferably 80 to 103° C. The aging step is not alwaysnecessary, however, in the case that the raw material liquid is a slurrycontaining precipitated particles, the precipitated particles grow andget stabilized by carrying out this step.

(Concentrating Step)

In the concentrating step, the raw material liquid is concentrated byheating it to evaporate the liquid in a concentrating tank. A targetviscosity or a target solid content at the time when the concentrationis finished is properly set according to a property of the raw materialliquid or a drying method after the concentration. The concentratingstep is not always necessary, however, physical properties of a driedpowder can be adjusted by carrying out this step. Further, there is acase that a reaction performance of the catalyst is improved by carryingout the concentrating step.

(Atomizing Step)

In the atomizing step, a solid matter contained in the raw materialliquid is atomized in an atomizing tank by using an atomizing measuresuch as homogenizer. The atomizing step is not always necessary,however, the reaction in the aging step is further advanced by carryingout this step.

(Drying, Heating, Molding, and the Like)

Further, a treatment such as drying, heating, and molding can be carriedout, when it is needed.

A device to be used for drying is not particularly limited, and forexample, a tray dryer, a spray dryer, a drum dryer, or a slurry dryercan be listed. Now, drying means an operation in which a substantiallysolid dried material is obtained by evaporating a part of or all theliquid from the raw material liquid. A drying temperature is preferably30 to 150° C. in the case of the tray dryer, and 100 to 500° C. as aninlet temperature in the case of the spray dryer. A shape of the driedmaterial is not particularly limited, and for example, a shape such aspowder or block can be listed.

In the case that the dried material does not have catalyst activity orimprovement of the catalyst activity is desired, it is possible to givethe catalyst activity by heating the dried material. A method forheating is not particularly limited, however, for example, a method ofpreliminary calcining at the temperature range of from 200 to 400° C.for about 1 to 5 hours followed by calcining at the temperature range offrom 400 to 650° C. for about 1 to 20 hours is preferable.

In the case of producing a molded catalyst, a dried material, a driedmaterial preliminary calcined, or a calcined material may be molded atan appropriate stage. A method for molding is not particularly limited,and for example, a molding method such as a supporting molding, apelleting molding, or an extrusion molding can be adopted.

(The Step of Washing with the Basic Solution)

In the present invention, a surface of at least one device equipped inan apparatus for the production of catalyst is washed with a basicsolution.

The surface of at least one device equipped in the catalyst productionapparatus means a surface to which a catalyst raw material to beintroduced at the time of catalyst production, a catalyst precursor, ora catalyst contacts. For example, an inner wall of a tank such as ablending tank, a mixing tank, an aging tank, a concentrating tank, or anatomizing tank; a surface of an internal device such as a stirringdevice or a heater used in the tank; an inner surface of an accessorydevice such as a strainer or a pump attached to the tank; an inner wallof a piping connected to the tank; a surface of a dryer which contactswith a material to be dried or a dried material; or a surface of amolding machine which contacts with a material to be molded or a moldedmaterial can be listed.

A solution or a slurry containing raw materials of molybdenum, bismuth,and iron and the like adheres to or remains in the form of pool on thesurface of such a device. There are many cases that such a liquidresidue becomes a solid matter and adheres to the surface of the deviceafter dried. Further, there is a case that a solid matter deposits onthe surface of the device from the solution or the slurry containing theraw materials and adheres to the surface of the device during thecatalyst production or after the catalyst production. Further, there isa case that an adherence to the surface of the device occurs through acontact with a solid matter already attached to the surface of thedevice. The solid matter usually contains molybdenum, bismuth, and iron.When the catalyst is produced again by using a device having a solution,a slurry, or a solid matter containing a catalyst raw material invarious states (hereinafter, also expressed collectively as a “residualmaterial”) on the surface of the device, the catalyst raw materialintroduced, the solution or the slurry each of which contains thecatalyst raw material, the catalyst precursor, or the catalyst contactsto the surface of the device. In the case of producing the catalystusing a device having such a residual material on the surface, thepresent invention is characterized by previously washing the surface ofthe device with a basic solution.

In the present invention, surfaces of all the devices having theresidual material may be washed with the basic solution, however, forexample, only specific devices such as a blending tank, a mixing tank,an aging tank, and a concentrating tank (hereinafter, expressedcollectively as “tanks”) may be washed. The present invention iseffective when washing with the basic solution is carried out to thetanks, and particularly effective when the washing with the basicsolution is carried out to any one of the mixing tank, the aging tank,and the concentrating tank. In this case, when there are internaldevices (a stirring blade and the like) of the tanks to be washed, it ispreferable to wash these internal devices and piping together with thetanks. Further, the present invention is effective when the residualmaterial is existing on the surface of the device as a solid matter. Assuch a solid matter, for example, one in which bismuth and iron form asolid solution with molybdenum trioxide can be listed.

When the amount of the residual material existing on the surface of thedevice (including the surface of the internal device when there is theinternal device) becomes large, there is a case that bulk density of thecatalyst powder obtained by at least one of drying and calcining the rawmaterial liquid increases and it becomes difficult to produce thecatalyst powder with excellent reproducibility. Further, there is a casethat the catalyst produced from such a catalyst powder has a lowactivity. These tendencies become more prominent when the amount of theresidual material exceeds 50 g per 1 m³ of the volume of the device. Asthis reason, it is presumed that a particle having a seed crystal of theresidual material generate in the raw material liquid and this particlecause the increase in the bulk density and the lowering of the catalystactivity. Consequently, the present invention is preferable when theamount of the residual material exceeds 50 g per 1 m³ of the volume ofthe device, and more preferable when the amount of the residual materialexceeds 100 g per 1 m³ of the volume of the device.

In the present invention, the surface of the device, on which theresidual material is existing, is washed with a basic solution. Themethod of washing is not particularly limited as long as the basicsolution contacts with the residual material, however, in the case ofthe tanks, a method of introducing the basic solution in the tanks andthen leaving the solution to stand or fluidizing the solution can belisted. When there is an internal device having the residual material onthe surface, it is preferable that washing be carried out in the stateof producing the catalyst, namely, in the state that the internal deviceis equipped. As the method of fluidizing the solution, for example, amethod of rotating a stirring blade or a method of circulating a liquidwith a pump can be listed.

The basic solution is not particularly limited as long as it is the oneobtained by dissolving a basic substance in a solvent. The basicsubstance contained in the basic solution may be one kind or two or morekinds. As the solvent of the basic solution, water, alcohol, or the likecan be listed, and water is preferable. As the basic substance, forexample, an oxide, a hydroxide, a carbonate, or a bicarbonate of analkaline metal such as lithium, sodium, potassium, or rubidium; or anoxide or a hydroxide of an alkaline earth metal such as magnesium,calcium, strontium, or barium can be listed. As the basic substance, atleast one kind selected from the group consisting of an oxide, ahydroxide, a carbonate, and a bicarbonate of an alkaline metal ispreferable, and a hydroxide of an alkaline metal is particularlypreferable. Further, as the alkaline metal, potassium is preferable.

The concentration of the basic substance in the basic solution ispreferably 1 to 10% by mass, and more preferably 2 to 6% by mass.

The temperature of the basic solution to be used for washing can beoptionally selected taking account of the extent of dissolution of theresidual material and the like, however, it is preferably 40 to 80° C.in point of washing effect, and more preferably 50 to 70° C.

The washing time is not particularly limited as long as it is enough forreducing the residual material, however, it is preferable to continuethe washing till the amount of the residual material existing on thesurface of the device becomes 50 g or less per 1 m³ of the volume of thedevice, more preferable to continue the washing till the amount of theresidual material existing on the surface of the device becomes 30 g orless, and furthermore preferable to continue the washing till theresidual material is perfectly removed or dissolved. It is preferable tocontinue the washing till the amount the residual material existing onthe surface of the device finally falls within the above range because apostwashing carried out after the washing with the basic solution cannotsubstantially remove the residual material. The concrete washing time isvariable depending on a kind or an amount of the residual material, oron a kind or an amount of the basic solution, and cannot be absolutelysaid, however, generally, it is preferably 1 to 5 hours and morepreferably 2 to 4 hours.

This washing can be carried out any one of under pressure aboveatmospheric pressure, under atmospheric pressure, and under reducedpressure below atmospheric pressure. It is preferable to carry out underthe reduced pressure from the viewpoint of absorption of vapor generatedby heating, and the like. The pressure inside the device when thewashing is carried out under the reduced pressure is preferably −0.05 to−0.001 MPa (gauge pressure).

Whether the residual material has been reduced by washing or not can bejudged through examination such as visual inspection of the surface ofthe device which was washed.

The mechanism of the reduction of the residual material by washing withthe basic solution is not clear, however, it is presumed that, when theresidual material contain a solid matter of a nitrate, the nitrate reactwith a basic substance to form a neutral salt which gradually removes ordissolves from the surface of the device into the basic solution.

In the case that the basic solution, even though once used for washing,has an ability to remove or dissolve the residual material, it ispreferable to reuse the basic solution in the next washing with thebasic solution because it can reduce waste.

(Postwashing Step by a Solvent)

In the present invention, it is preferable that washing a surface of adevice with a solvent (hereinafter, expressed as a “postwashing”) becarried out after washing of the surface of the device with the basicsolution be carried out. The method for the postwashing is notparticularly limited as long as the solvent contacts with the surface ofthe device which is washed with the basic solution, however, in the caseof the postwashing of the tanks, a method of introducing the solvent inthe tanks and then leaving the solvent to stand or fluidizing thesolvent can be listed. In the case that the device has an internaldevice and washing with the basic solution has been carried out in thestate that the internal device is equipped, it is preferable that thepostwashing be carried out in the state that the internal device isequipped. As the method for fluidizing the solvent, for example, amethod of rotating a stirring blade or a method of circulating a liquidwith a pump can be listed.

The solvent to be used for the postwashing is not particularly limitedas long as it can remove a metal ion contained in the basic solutionsuch as an alkaline metal or an alkaline earth metal, however, water ispreferable. As the water, for example, a pure water, an ion-exchangedwater, a distilled water, or a running water can be listed, however, onethat contains little amount of sodium ion or calcium ion is preferable.The electric conductivity at 25° C. of the water to be used for thepostwashing is more preferably not more than 10 mS/m and particularlypreferably not more than 1 mS/m.

The temperature of the solvent to be used for the postwashing can beoptionally selected taking account of the extent of remaining amount ofthe basic solution and the like, however, it is preferably within therange of from 20° C. to the boiling point of the solvent in point ofwashing effect, and more preferably within the range of from 50° C. tothe boiling point of the solvent.

When the postwashing is carried out using water as the solvent, namely,washing with water is carried out, it is preferable to continue orrepeat the washing with water till pH of the wastewater at 50° C. afterthe washing with water becomes 9 or less, more preferable to continue orrepeat till pH at 50° C. becomes 4 to 9, and furthermore preferable tocontinue or repeat till pH at 50° C. becomes 6 to 8. Further, it ispreferable to continue or repeat the postwashing till the sum ofconcentrations of an alkaline metal and an alkaline earth metal in thewastewater becomes 50 mg/liter or less, and more preferable to continueor repeat till the sum becomes 10 mg/liter or less.

The postwashing can be carried out any one of under pressure aboveatmospheric pressure, under atmospheric pressure, and under reducedpressure below atmospheric pressure. It is preferable to carry out underthe reduced pressure from the viewpoint of absorption of vapor generatedby heating, and the like. The pressure inside the device when thepostwashing is carried out under the reduced pressure is preferably−0.05 to −0.001 MPa (gauge pressure).

(Prewashing Step by a Solvent)

In the present invention, it is preferable that washing a surface of adevice with a solvent (hereinafter, expressed as a “prewashing”) bepreviously carried out before washing of the surface of the device withthe basic solution be carried out. The method for the prewashing is notparticularly limited as long as the solvent contacts with the surface ofthe device having the residual material, however, in the case of theprewashing of the tanks, a method of introducing the solvent in thetanks and then leaving the solvent to stand or fluidizing the solventcan be listed. In the case that there is an internal device having theresidual material on the surface, it is preferable that the prewashingbe carried out in the state that the internal device is equipped. As themethod for fluidizing the solvent, for example, a method of rotating astirring blade or a method of circulating a liquid with a pump can belisted.

The solvent to be used for the prewashing is preferably one that canremove or dissolve a part of the residual material, and more preferablywater. As the water, for example, a pure water, an ion-exchanged water,a distilled water, or a running water can be listed, however, one thatcontains little amount of sodium ion or calcium ion is preferable. Theelectric conductivity at 25° C. of the water to be used for theprewashing is preferably not more than 10 mS/m and particularlypreferably not more than 1 mS/m. It is preferable to remove a part ofthe residual material by the prewashing because it can reduce the amountof the basic solution to be used.

The temperature of the solvent to be used for the prewashing can beoptionally selected taking account of the extent of dissolution of theresidual material and the like, however, it is preferably within therange of from 20° C. to the boiling point of the solvent in point ofwashing effect, more preferably within the range of from 50° C. to theboiling point of the solvent, and particularly preferably within therange of from 80° C. to the boiling point of the solvent.

The prewashing can be carried out any one of under pressure aboveatmospheric pressure, under atmospheric pressure, and under reducedpressure below atmospheric pressure. It is preferable to carry out underthe reduced pressure from the viewpoint of absorption of vapor generatedby heating, and the like. The pressure inside the device when theprewashing is carried out under the reduced pressure is preferably −0.05to −0.001 MPa (gauge pressure).

(Method for Using the Catalyst)

In the next place, the method for using the catalyst will be explained.It is preferable that the catalyst be used in a molded form or asupported form in a fixed bed, however, the catalyst may be used in aparticle form in a fluidized bed. Reaction conditions will be explainedusing, as an example, the cases in which, by using this catalyst, anoxidation reaction of isobutylene, TBA, or MTBE (hereinafter, alsoexpressed collectively as “isobutylene or the like”) to methacrolein andmethacrylic acid (hereinafter, also expressed collectively as“methacrolein and the like”) and an oxidation reaction of propylene toacrolein and acrylic acid (hereinafter, also expressed collectively as“acrolein and the like”) are carried out.

When the oxidation reaction of the isobutylene or the like to themethacrolein and the like is carried out, a feed gas containing theisobutylene or the like and molecular oxygen is brought into contactwith the catalyst. The concentration of the isobutylene or the like inthe feed gas is preferably 1 to 20% by volume, and the molar ratio ofthe isobutylene or the like to oxygen is preferably 1/0.5 to 1/3. Watervapor may be added to the feed gas, and the concentration of the watervapor is preferably 1 to 45% by volume. Further, the reaction pressureis preferably 0 to 300 kPa (gauge pressure), and the reactiontemperature is preferably 250 to 400° C., and the contact time ispreferably 1.5 to 15 seconds.

When the oxidation reaction of propylene to acrolein and the like iscarried out, a feed gas containing propylene and molecular oxygen isbrought into contact with the catalyst. The concentration of propylenein the feed gas is preferably 1 to 20% by volume, and the molar ratio ofpropylene to oxygen is preferably 1/0.5 to 1/3. Water vapor may be addedto the feed gas, and the concentration of the water vapor is preferably1 to 45% by volume. Further, the reaction pressure is preferably 0 to300 kPa (gauge pressure), and the reaction temperature is preferably 250to 400° C., and the contact time is preferably 1.5 to 15 seconds.

EXAMPLES

Hereinafter, the present invention will be explained by examples andcomparative examples.

Isobutylene conversion, selectivity to methacrolein, selectivity tomethacrylic acid, and total yield of methacrolein and methacrylic acid(hereinafter, expressed as a “total yield”) were calculated by thefollowing formulae.

Isobutylene conversion (%)=(A/B)×100

Selectivity to methacrolein (%)=(C/A)×100

Selectivity to methacrylic acid (%)=(D/A)×100

Total yield (%)={(C+D)/B}×100

In the above formulae, A represents number of moles of isobutylenereacted, B represents number of moles of isobutylene supplied, Crepresents number of moles of methacrolein produced, and D representsnumber of moles of methacrylic acid produced. The analysis was carriedout using gas chromatography.

Further, reaction rate (catalyst activity) per mass of catalyst is aflow rate of a raw material per mass of catalyst and time (NL/kg·h)under the conditions that reaction temperature is fixed and conversionof isobutylene which is a raw material is approximately fixed.

Reference Example 1

To blending tank 1, 1,000 parts of pure water was introduced, and 500parts of ammonium paramolybdate, 18.5 parts of ammonium paratungstate,24.1 parts of antimony trioxide, 14.3 parts of potassium nitrate, and496.3 parts of 20% by mass silica sol were added, and the resultantmixture was heated while stirred to prepare liquid A which is a blendedliquid.

To blending tank 2, 850 parts of pure water was introduced, and 250parts of 60% by mass nitric acid was added and the resultant solutionwas made homogeneous, and 57.2 parts of bismuth nitrate was added anddissolved. To the resultant solution, 228.8 parts of ferric nitrate,494.4 parts of cobalt nitrate, and 77.2 parts of zinc nitrate weresuccessively added and dissolved to prepare liquid B which is a blendedliquid.

Using the blending tank 1 as a mixing tank, the liquid B was added whilethe liquid A was stirred to obtain a raw material liquid in a state ofslurry. The raw material liquid was transferred to a aging tank, heatedto 95° C., and aging of the raw material liquid was carried out for 90minutes. Subsequently, using the aging tank as a concentrating tank,concentration of the raw material liquid which had been aged was carriedout at 103° C.

Subsequently, the concentrated raw material liquid was drawn out fromthe concentrating tank, and made into dried spherical particles using aspray dryer. The spherical particles were preliminarily calcined at 300°C. for 1 hour, and further calcined at 500° C. for 3 hours to obtain acalcined catalyst (catalyst powder). The average particle diameter ofthe calcined catalyst was 54 μm, and the bulk density of the calcinedcatalyst was 1.00 g/ml. The average particle diameter was measured bylaser diffraction type and on the basis of volume, and the bulk densitywas measured according to the method described in JIS K6721.

To 500 parts of the calcined catalyst, 15 parts of methyl cellulose wasadded and dryblended. To the resultant mixture, 180 parts of pure waterwas added and mixed (kneaded) with a kneader, and then extrusion moldedwith a piston type extrusion molder to obtain ring shaped moldedarticles of external diameter of 5 mm, internal diameter of 2 mm, andlength of 5 mm.

The resultant molded articles were dried at 110° C. with a circulatinghot air dryer, and calcined again at 400° C. for 3 hours to obtain acatalyst. The composition of elements excluding oxygen of the catalystthus obtained was Mo₁₂ Bi_(0.5) Fe_(2.4) Co_(7.2) Zn_(1.1) Sb_(0.7) Si₇W_(0.3) K_(0.5).

The catalyst was packed in a stainless steel reaction tube and reactionwas carried out using a feed gas containing 5% of isobutylene, 12% ofoxygen, 10% of water vapor, and 73% of nitrogen (volume %), under theconditions of under atmospheric pressure, contact time of 3.6 seconds,and reaction temperature of 340° C., until isobutylene conversion became95%. As a result, the selectivity to methacrolein was 88.8%, theselectivity to methacrylic acid was 4.0%, the total yield ofmethacrolein and methacrylic acid was 88.2%, and the catalyst activitywas 2,300 NL/kg·h.

Example 1

On the surfaces of the blending tank 1 and the aging tank used for thecatalyst production in Reference Example 1 (including the surface of astirring device equipped inside), 120 g of the residual materialcontaining molybdenum, bismuth, and iron per 1 m³ of each volume of theblending tank 1 and the aging tank existed, respectively. The fact thatmolybdenum, bismuth, and iron were contained in the residual materialwas confirmed with ICP spectrometry. Further, the amount of the residualmaterial was quantitatively determined in such a way that the catalystwas previously produced by separately carrying out the same operation,and the residual material was carefully scraped up from the surfaces ofthe blending tank 1 and the aging tank.

To the blending tank 1, on the surface of which there exists theresidual material, 0.98 time as much as the volume of the blending tank1 of pure water at 60° C. (electric conductivity at 25° C. being 4 mS/m)was introduced, and a prewashing was carried out once for 60 minutesunder stirring. The prewashing was carried out adjusting the pressureinside the blending tank 1 to −0.01 MPa (gauge pressure).

Subsequently, after all the pure water used for the prewashing in theblending tank 1 was discharged, 0.98 time as much as the volume of theblending tank 1 of 4% by mass potassium hydroxide aqueous solution at60° C. was introduced to the blending tank 1, and the blending tank 1was washed for 1 hour while stirred with a stirrer. The washing with abasic solution was carried out adjusting the pressure inside theblending tank 1 to −0.01 MPa (gauge pressure).

Subsequently, after all the potassium hydroxide aqueous solution usedfor washing in the blending tank 1 was discharged, 0.98 time as much asthe volume of the blending tank 1 of pure water at 100° C. (electricconductivity at 25° C. being 4 mS/m) was introduced to the blending tank1, and a postwashing was carried out once for 60 minutes under stirring.The postwashing was carried out adjusting the pressure inside theblending tank 1 to −0.01 MPa (gauge pressure).

The pH of the wastewater at 50° C. after the postwashing was 6.2, andthe total concentration of an alkaline metal and an alkaline earth metalin the wastewater was 22 mg/liter. Further, the amount of the residualmaterial, containing molybdenum, bismuth, and iron, existing on thesurface of the inner wall of the blending tank 1 after the postwashingwas 36 g per 1 m³ of the volume of the blending tank 1.

Further, washing of the aging tank was carried out using the sameprocedure as in washing of the blending tank 1. As a result, the pH ofthe wastewater at 50° C. after the postwashing was 6.5, and the totalconcentration of an alkaline metal and an alkaline earth metal in thewastewater was 25 mg/liter. Further, the amount of the residualmaterial, containing molybdenum, bismuth, and iron, existing on thesurface of the inner wall of the aging tank after the postwashing was 40g per 1 m³ of the volume of the aging tank.

Using the blending tank 1 and the aging tank washed as mentioned above,the catalyst was produced in the same manner as in Reference Example 1,and the reaction producing methacrolein and methacrylic acid fromisobutylene was carried out.

Example 2

The blending tank 1 and the aging tank which were used for producing thecatalyst in Example 1 were washed in the same manner as in Example 1.The states of the wastewater after washing, the blending tank 1, and theaging tank were about the same as those in the case of Example 1. Thesame procedure as in Reference Example 1 was carried out except that theblending tank 1 and the aging tank thus washed were used, and thecatalyst of the second batch was produced, and the reaction producingmethacrolein and methacrylic acid from isobutylene was carried out.

Example 3

The blending tank 1 and the aging tank which were used for producing thecatalyst in Example 2 were washed in the same manner as in Example 1.The states of the wastewater after washing, the blending tank 1, and theaging tank were about the same as those in the case of Example 1. Thesame procedure as in Reference Example 1 was carried out except that theblending tank 1 and the aging tank thus washed were used, and thecatalyst of the third batch was produced, and the reaction producingmethacrolein and methacrylic acid from isobutylene was carried out.

Example 4

The blending tank 1 and the aging tank which were used for producing thecatalyst in Example 3 were washed in the same manner as in Example 1.The states of the wastewater after washing, the blending tank 1, and theaging tank were about the same as those in the case of Example 1. Thesame procedure as in Reference Example 1 was carried out except that theblending tank 1 and the aging tank thus washed were used, and thecatalyst of the fourth batch was produced, and the reaction producingmethacrolein and methacrylic acid from isobutylene was carried out.

Reference Example 2

The catalyst was produced in totally the same manner as in ReferenceExample 1, and the reaction producing methacrolein and methacrylic acidfrom isobutylene was carried out.

Comparative Examples 1 to 4

Washing was carried out in the same manner as in Example 1 except thatthe blending tank 1 and the aging tank which were used for producing thecatalyst in Reference Example 2 were washed with pure water (electricconductivity at 25° C. being 4 mS/m) instead of 4% by mass potassiumhydroxide aqueous solution. The same procedure as in Reference Example 1was carried out except that the blending tank 1 and the aging tank thuswashed were used, and the catalyst was produced, and the reactionproducing methacrolein and methacrylic acid from isobutylene was carriedout (Comparative Example 1). Further, the same procedures wererepeatedly carried out in washing of the blending tank 1 and the agingtank, production of the catalyst, and the reaction producingmethacrolein and methacrylic acid from isobutylene as in Examples 2 to4, except that pure water was used instead of 4% by mass potassiumhydroxide aqueous solution (Comparative Examples 2 to 4). The amount ofa material adhered to the blending tank 1 and the aging tank increasedas the number of times of the batch.

The results of the examples and the comparative examples mentioned aboveare collectively shown in Table 1.

TABLE 1 Catalyst Selectivity to Selectivity to Bulk density of activitymethacrolein methacrylic Total yield catalyst (NL/kg · h) (%) acid (%)(%) powder (g/ml) Reference Ex. 1 2,300 88.8 4.0 88.2 1.00 Example 12,250 88.7 4.0 88.1 0.99 Example 2 2,310 88.7 4.1 88.2 0.99 Example 32,330 88.7 4.1 88.2 1.00 Example 4 2,290 88.8 3.9 88.1 0.98 ReferenceEx. 2 2,300 88.8 4.0 88.2 1.00 Comparative Ex. 1 1,396 88.6 4.0 88.01.10 Comparative Ex. 2 1,793 88.5 3.9 87.8 1.13 Comparative Ex. 3 2,10088.5 3.8 87.7 1.15 Comparative Ex. 4 1,150 88.4 3.8 87.6 1.19

In the examples, the catalyst activity, the selectivity to methacrolein,and the selectivity to methacrylic acid were obtained with excellentreproducibility. Further, the bulk density of the catalyst powder wasstable. On the other hand, in the comparative examples, the catalystactivity, the selectivity to methacrolein, and the selectivity tomethacrylic acid were bad in reproducibility, and the bulk density ofthe catalyst powder became larger as the number of times of the batch.

1. A method for producing a catalyst comprising molybdenum, bismuth, andiron, comprising the steps of: washing a surface of at least one deviceequipped in an apparatus for the production of catalyst, to which asolid matter adheres, with a basic solution; and producing the catalystwith the apparatus for the production of catalyst thus washed.
 2. Themethod for producing a catalyst according to claim 1, wherein thecatalyst is used for producing an unsaturated aldehyde and anunsaturated carboxylic acid through gas-phase catalytic oxidation ofpropylene, isobutylene, tertiary butyl alcohol, or methyl tertiary butylether with molecular oxygen.
 3. The method for producing a catalystaccording to claim 1, wherein the catalyst is used for producing anunsaturated nitrile through gas-phase catalytic ammoxidation ofpropylene, isobutylene, or tertiary butyl alcohol with molecular oxygenand ammonia.
 4. The method for producing a catalyst according to claim1, wherein the basic solution is the one obtained by dissolving at leastone selected from the group consisting of an oxide, a hydroxide, acarbonate, and bicarbonate of an alkaline metal, and an oxide and ahydroxide of an alkaline earth metal in a solvent.
 5. The method forproducing a catalyst according to claim 1, wherein the washing with thebasic solution is carried out till the solid matter adhering to thesurface of the device to be washed in the step of washing with the basicsolution becomes 50 g or less per 1 m³ of the volume of the device. 6.The method for producing a catalyst according to claim 1, wherein thedevice to be washed in the step of washing with the basic solution isselected from a mixing tank in which a raw material liquid comprisingall the elements composing the catalyst is prepared, an aging tank inwhich the raw material liquid is aged while heated, and a concentratingtank in which the raw material liquid is concentrated, and washedtogether with an internal device and a piping of the device.
 7. Themethod for producing a catalyst according to claim 1, wherein the stepof washing with the basic solution is carried out under reducedpressure.
 8. The method for producing a catalyst according to claim 1,further comprising the step of washing the surface of the device to bewashed in the step of washing with the basic solution with a solvent, atleast one of before the step of washing with the basic solution andafter the step of washing with the basic solution.
 9. The method forproducing a catalyst according to claim 8, wherein the solvent is water.10. The method for producing a catalyst according to claim 9, whereinthe water has an electric conductivity of not more than 10 mS/m.
 11. Themethod for producing a catalyst according to claim 9, wherein thewashing with water is carried out after the step of washing with thebasic solution till pH of a wastewater at 50° C. becomes 9 or less. 12.The method for producing a catalyst according to claim 9, wherein thewashing with water is carried out after the step of washing with thebasic solution till a total concentration of an alkaline metal and analkaline earth metal in the wastewater becomes 50 mg/liter or less. 13.The method for producing a catalyst according to claim 8, wherein thestep of washing with the solvent is carried out under reduced pressure.